The invention relates to a method for positional determination for an EC motor on a device for the adjustment of the rotational angular position of the camshaft of a reciprocating piston combustion engine relative to the crankshaft, wherein the crankshaft is in driving connection with the camshaft via an adjustment mechanism, which is constructed as a triple-shaft transmission with a crankshaft-fixed drive shaft, a camshaft-fixed driven shaft, and an adjustment shaft, which is in driving connection with the EC motor, wherein the rotor of the EC motor has magnetic segments offset relative to each other in the peripheral direction and magnetized alternately in directions opposite each other, wherein for determining the position of the rotor relative to the stator of the EC motor, a measurement device is provided, which has magnetic field sensors, which are offset relative to each other in the peripheral direction and which are arranged such that, for an error-free measurement during rotational movement of the rotor relative to the stator, they generate a digital sensor signal, which cycles through a sequence of sensor signal states, wherein this sequence occurs at least twice for each mechanical rotation of the rotor.
Such a method for determining the position of the rotor of an EC motor relative to its stator is known from practice. Here, the EC motor is a part of a camshaft adjustment device, by means of which the rotational angular position of the camshaft of a reciprocating piston combustion engine relative to the crankshaft is adjustable. The camshaft adjustment device has an adjustment mechanism, which is constructed as a triple-shaft transmission, with whose drive shaft a camshaft gear that is rotatably supported relative to the camshaft is locked in rotation, which is in driving connection with a crankshaft gear via a drive chain. A driven shaft of the adjustment mechanism is in driving connection with the camshaft and an adjustment shaft with the EC motor. For a stationary drive shaft, between the adjustment shaft and the driven shaft there is a transmission gear ratio, the so-called stationary transmission gear ratio, given by the adjustment mechanism. If the adjustment shaft rotates, then the phase position of the camshaft relative to the crankshaft increases or decreases according to the rotational direction of the adjustment shaft. In comparison with an internal combustion engine that is operated at a constant phase position, a better filling of the cylinders of the internal combustion engine can be achieved by adapting the phase position, whereby fuel is saved, the emission of pollutants is reduced, and/or the output power of the internal combustion engine can be increased.
The position of the rotor relative to the stator is measured with the help of a measurement device that has three Hall sensors, which are connected rigidly to the stator and which are distributed over the periphery of the stator. The magnetic field of the projecting magnetic segments of the rotor flows through the Hall sensors during a rotational movement between the stator and rotor. The magnetic fields of the magnetic segments induce electrical voltages, which are usable as digital sensor signals for a positional measurement, in the Hall sensors. For the positional measurement, initially a positional measurement signal is set to a start value and then the rotor is rotated relative to the stator, wherein the positional measurement signal tracked for each occurrence of a state change of the sensor signal. The positional measurement signal is fed to a control device, which energies the individual phases of the winding, such that an alternating magnetic field, which drives the rotor is formed between the stator and the rotor. The EC motor and the measurement device, however, are in practice exposed to interference radiation, which comes into the measurement device, for example, via power-supply lines, and can cause errors in the positional measurement signal. Here, it can occur on one hand that due to interference, one or more state changes are not taken into consideration during the tracking of the positional measurement signal. On the other hand, however, it is also possible that too many state changes are detected during the tracking of the positional measurement signal. In both cases, the positional measurement signal deviates from the actual position of the rotor, so that the rotor is not properly energized. Therefore, torque losses, uneven engine running, and errors in the adjustment of the rotational angular position of the camshaft relative to the crankshaft can occur.